1. FIELD OF THE INVENTION
This invention relates to a tethered surveillance balloon. More particularly, this invention relates to a tethered surveillance balloon having an inflatable main body in combination with an aerodynamic lifting device.
2. DESCRIPTION OF RELATED ART
Gas filled surveillance balloons have been utilized for quite sometime for military and research purposes. In fact, gas observation platforms were used by both sides in the American Civil War and again in World War I. Such balloons were generally gas filled and anchored to the ground by long cables. With the development of planes during the later stages of World War I, gas filled balloons were generally less relied upon. Gas filled balloons, however, made a comeback in World War II when barrage balloons were used to protect ships and cities from aerial attack. The "Caquot" type balloon was used extensively during World War II as an aerial observation post and also as a barrage balloon. "Caquot" balloons were designed to withstand winds of about 50 miles per hour and rise to heights of about 6,000 feet. When in use as barrage balloons, a plurality of the gas filled balloons were held captive by steel anchor wires arranged to form a curtain which posed a serious hazard to low flying enemy aircraft. Nonetheless, to maintain the desired height while withstanding winds of about 50 miles per hour, the balloons required a high lift-to-weight ratio. To achieve this relatively high lift-to-weight ratio, the balloons had to be formed of relatively large volumes. These balloons were thus easy to spot both from the ground and in the air.
U.S. Pat. No. 870,430 to Herve discloses a captive observation balloon used for military or scientific purposes. The balloon includes an elongated body having a plurality of interconnected auxiliary gas filled chambers at its aft end to stabilize the captive balloon. Like the Caquot balloon, the Herve balloon relied upon a high lift-to-weight ratio, to achieve the desired height. In order to achieve this high lift-to-weight ratio, the balloon was formed with a relatively large volume making detection and destruction (at least when used for military purposes) easy.
Prior art balloons were also not radar transparent and were often formed of a material which did not blend into the background. The requirement for a large volume balloon also necessitated large storage facilities and made transportation more costly and difficult. Furthermore, since the amount of gas necessary to fill the balloon is directly proportional to its volume, the large volume prior art balloons were expensive to fill with gases such as hydrogen and helium.
Any attempt to reduce the volume of the prior art inflatable balloons resulted in a decrease in the lift-to-weight ratio. Thus, although a reduced volume observation balloon having the general structure as that of the prior art might achieve sufficient height in still air, high wind conditions would result in both a drifting and a decrease in altitude. A decrease in altitude would also make the observation balloon more easy to detect and destroy when utilized for military purposes.